For electrons in solids it is well known that quantum many-body interactions cause material properties such as conductivity and magnetism. For atoms in a gas, however, it is difficult to observe quantum many-body effects unless the atoms are very cold, because hot atoms behave more like ordinary ballistic particles. This project will cool lithium atoms below one millionth of a degree Kelvin and manipulate gases of ultra-cold atoms in optical traps in order to study how quantum mechanics influences large collections of atoms. This will advance the science known as quantum many-body physics. The advantage of using ultra-cold atoms is that their temperature, density, and traps can be readily controlled and adjusted. This is important because it will help physicists understand phenomena such as superconductivity and exotic types of magnetism. In particular, this project will study how magnetism and superconductivity co-exist. This will improve the fundamental understanding of high-temperature superconductors, and may enable fabrication of new materials that superconduct at even higher temperatures. Another part of this project will probe how quantum many-body phenomena affect the propagation of collective waves known as solitons. This part of the project is important because it could lead to improved sensors.
Both parts of this project will use an isotope of lithium, in one case a boson, while in the other a fermion. The goal of the proposed boson experiment is to explore the role of near-integrability in bright matter-wave solitons, either fundamental ones or higher-order soliton breathers. The plan is to create a breather using a protocol developed by theoretical collaborators, and to explore its interactions with a beam splitter formed from a blue-detuned light sheet. The goals are both fundamental and technological. One goal is to create a mesoscopic (N = 100-300) quantum object and observe its properties in a novel one-dimensional interferometer using the light sheet as a beam splitter. If the center-of-mass energy of the soliton is below the binding energy of a single atom, it will not fragment upon interacting with the beam splitter, but rather tunnel and reflect in its entirety, thus creating a Schrödinger cat state. In the second part of this project, this laboratory will implement new ideas for creating and directly detecting the exotic superconducting state known as FFLO (Fulde-Ferrell-Larkin-Ovchinnikov state) with a spin-imbalanced Fermi gas. While FFLO is prevalent in 1D, both quantum and thermal fluctuations tend to destroy long-range order in lower dimensions. The recent determination from this laboratory of the phase diagram of the 1D-3D dimensional crossover in a gas of spin-polarized fermions points to a region in parameter space where FFLO is both prevalent and stable. The next goal for this team is to detect the periodic domain walls occupied by the unpaired fermions in time-of-flight expansion in 1D. This would constitute the first direct evidence for FFLO.
